Evaluation of Interfacial Shear Strength Healing Efficiency between Dynamic Covalent Bond-Based Epoxy and Functionalized Fiberglass

Extending the service life of light-weight composite materials used in structural applications has drawn extensive research interests in recent years. One promising solution is the incorporation of self-healing polymers as the matrix component to enable the intrinsic repair of structural damage, thus allowing the composite structure to maintain its mechanical performance and expand its useful life. One of the primary failure mechanisms in composites is interfacial failure, and this research seeks to develop a methodology that enables reformation of covalent crosslinks at the interface to recover material strength. The approach developed here focuses on the evaluation of interfacial shear strength (IFSS) of a composite material system consisting of a self-healing matrix formed by bisphenol-F diglycidyl ether mixed with 4-aminophenyl disulfide (4-AFD) and fiberglass. Interfacial damage is repaired through thermal stimulus that cleaves the dynamic covalent disulfide bonds in the 4-AFD constituent of the matrix followed by bond reformation to return material strength. The extent of interfacial healing was characterized through repeated microdroplet testing and was measured to be 61.7 and 39.7% for once- and twice-healed microdroplets, respectively, thus demonstrating the potential of the chosen composite system to not only exhibit matrix healing, as reported in most studies, on self-healing composites but also at the fiber–matrix interface. The surface chemistry of the glass fibers was modified through silane coupling agents 3-(glycidoxypropyl)trimethoxysilane and bis(triethoxysilylpropyl)tetrasulfide (Si-69) functionalization, and their subsequent effects on the IFSS and healing efficiency of the fiber–matrix system were investigated. The Si-69-functionalized fiberglass exhibited an enhancement in IFSS of 31.5% due to the improved fiber–matrix chemical interactions because of the increase in surface functional group concentrations. Therefore, this work demonstrates the interfacial healing potential of 4-AFD-based polymer matrices when incorporated in glass fiber composites and highlights the promising effects of surface functionalization for simultaneously improving IFSS and maintaining interfacial healing efficiency.